This invention is generally directed to processes for the preparation of toner and developer compositions, and more specifically, the present invention is directed to processes for the preparation of magnetic toners containing coupling agents. In one embodiment, there are provided in accordance with the present invention processes for the preparation of toner compositions comprised of resin particles, pigment particles, charge enhancing additives, and a coupling agent, especially organotitanate coupling agents, which processes in an embodiment comprises extruding the toner components while injecting water therein. In one embodiment, the economical process of the present invention comprises introducing a coupling agent and water into a toner blend during the melt mixing step accomplished, for example, in a known toner extruder, such as the ZSK-53 manufactured by Werner-Fleiderer. Advantages associated with the process of the present invention in embodiments thereof include use of economical, readily available magnetites, and coupling agents, which components can, for example, be significantly lower in cost than that of pretreated magnetite; the process is readily adaptable to a variety of pigments including carbon black and color pigments; a reduction in the extruder torque; the injecting of water into the extruder causes a reduction in temperature, facilitates scavenging unreacted coupling agent and provides for the removal of volatile impurities.
In an embodiment, the process of the present invention comprises introducing a known coupling agent to a preblended mixture of toner constituents comprised, for example, of resin particles and pigment particles prior to extrusion. More specifically, the coupling agent can initially be adsorbed onto a substrate such as silica, and the resulting modified silica powder can then be added to the other toner components. This embodiment has the added advantage of improving the preblend powder flow which is to be fed to the extruder. Also, by adsorbing the coupling agent onto the substrate, its inclusion in the melt mix process can be facilitated.
The toners obtained with the process of the present invention can be selected for a number of imaging methods, including xerographic imaging and printing processes wherein latent images are developed and transferred to supporting substrates such as paper.
Processes for the preparation of toner compositions by melt blending and extrusion are well known. In these processes, polymer, pigment, additive, and the like can be added to a melt mixing apparatus, such as a Banbury Mill, followed by heating at a temperature, for example, of above 120.degree. C., cooling, micronization of the resulting toner, followed by classification to provide toner particles with an average particle diameter of from about 10 to about 25 microns. In U.S. Pat. No. 4,600,676, the disclosure of which is totally incorporated herein by reference, there is illustrated the preparation of toners directly by polymerizing a monomer in the presence of a titanate coupling agent, see the Abstract for example. In column 10 of this patent, it is indicated that the titanate coupling agent is present in the polymerization reaction at the time of reaction, and in Example 1, column 16, an aqueous polyvinyl alcohol solution is selected as part of the reaction mixture. In U.S. Pat. No. 4,450,221, the disclosure of which is totally incorporated herein by reference, there is illustrated the preparation of single component toners wherein there is selected a magnetite rendered hydrophobic by surface treatment with a titanium, or silicone coupling agent. The '221 patent discloses magnetites which have been pretreated with coupling agent. One disadvantage of using a pretreated magnetite relates to its cost, about 1.5 to 3 times higher in cost, as compared to untreated magnetites. Furthermore, commercial sources for pretreated magnetites with magnetic and lyophilic properties that are suitable for a number of xerographic toner compositions is limited. By treating the magnetite with coupling agent during toner fabrication, therefore, greater flexibility in choice of magnetite and coupling agent can be achieved.
Also, developer compositions with charge enhancing additives, which impart a positive charge to the toner resin, are known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions. In this patent, there are disclosed quaternary ammonium compounds with four R substituents on the nitrogen atom, which substituents represent an aliphatic hydrocarbon group having 7 or less, and preferably about 3 to about 7 carbon atoms, including straight and branch chain aliphatic hydrocarbon atoms, and wherein X represents an anionic function. According to this patent, a variety of conventional anionic moieties such as halides, phosphates, acetates, nitrates, benzoates, methylsulfates, perchloride, tetrafluoroborate, benzene sulfonate, and the like can be selected. U.S. Pat. No. 4,221,856 discloses electrophotographic toners containing resin compatible quaternary ammonium compounds in which at least two R radicals are hydrocarbons having from 8 to about 22 carbon atoms, each other R is a hydrogen or hydrocarbon radical with from 1 to about 8 carbon atoms, and A is an anion, for example sulfate, sulfonate, nitrate, borate, chlorate, and the halogens such as iodide, chloride and bromide, reference the Abstract of the Disclosure and column 3; a similar teaching is presented in U.S. Pat. No. 4,312,933, which is a division of U.S. Pat. No. 4,291,111; and similar teachings are presented in U.S. Pat. No. 4,291,112 wherein A is an anion including, for example, sulfate, sulfonate, nitrate, borate, chlorate, and the halogens. There are also described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of electrostatic latent images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica. The aforementioned toners are usually prepared by melt blending processes as mentioned herein.
Also, there are disclosed in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, developer compositions containing as charge enhancing additives organic sulfate and sulfonates, which additives can impart a positive charge to the toner composition. Further, there are disclosed in U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions with resin particles and pigment particles, and as charge enhancing additives alkyl pyridinium compounds. Additionally, other documents disclosing positively charged toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014; 4,394,430 and 4,560,635 which illustrate a toner with a distearyl dimethyl ammonium methyl sulfate charge additive. One disadvantage that may be associated with the charge additive of the '635 patent resides in its apparent inherent instability in some instances as the additive may thermally and chemically degrade, and react with other toner components.
The following prior art, all United States patents, is mentioned, and wherein the toners indicated can be prepared by known melt blending and extrusion methods: U.S. Pat. No. 4,812,381 which discloses toners and developers containing charge control agents comprising quaternary ammonium salts of the formula indicated, for example, in the Abstract of the Disclosure, wherein R is alkyl with from 12 to 18 carbon atoms, and the anion is a trifluoromethyl sulfonate; also note, for example, the information presented in columns 2 and 3 of this patent; a similar teaching is presented U.S. Pat. No. 4,834,921; U.S. Pat. No. 4,490,455 which discloses toners with, for example, amine salt charge enhancing additives, reference the Abstract of the Disclosure for example, and wherein A is an anion including those derived from aromatic substituted sulfonic acids, such as benzene sulfonic acid, and the like, see column 3, beginning at line 33; U.S. Pat. No. 4,221,856 directed to toners with a quaternary ammonium compound wherein A is an anion such as sulfate, sulfonate, nitrate, borate, chlorate, and certain halogens, see the Abstract of the Disclosure; Reissue 32,883 (a reissue of U.S. Pat. No. 4,338,390) illustrates toners with sulfate and sulfonate charge additives, see the Abstract of the Disclosure, wherein R.sub.4 is an alkylene, and the anion contains a R.sub.5 which is a tolyl group, or an alkyl group of from 1 to 3 carbon atoms, and n is the number 3; U.S. Pat. No. 4,323,634 which discloses toners with charge additives of the formulas presented in column 3, wherein at least one of the R's is a long chain amido group, and X is a halide ion or an organosulfur containing group, U.S. Pat. No. 4,326,019 relating to toners with long chain hydrazinium compounds, wherein the anion A can be a sulfate, sulfonate, phosphate, halides, or nitrate, see the Abstract of the Disclosure for example; U.S. Pat. No. 4,752,550 which illustrates toners with inner salt charge additives or mixtures of charge additives, see for example column 8; U.S. Pat. No. 4,684,596 which discloses toners with charge additives of the formula provided in column 3, wherein X can be a variety of anions such as trifluoromethane sulfonate; and U.S. Pat. Nos. 4,604,338; 4,792,513; 3,893,935; 4,826,749 and 4,604,338, the disclosure of each of the aforementioned patents being totally incorporated herein by reference.
The following prior art, all U.S. patents, is mentioned: U.S. Pat. No. 4,812,381 relating to toners and developers with quaternary ammonium salts of the formula illustrated in column 3, the preparation thereof, see column 4, and also note the working Examples, columns 7 and 8, wherein specific charge additives, such as octadecyl ammonium trifluoromethane sulfonate, are reported; U.S. Pat. No. 4,675,118 which discloses certain quaternary salts as fabric softeners, see the Abstract of the Disclosure, and note column 1, for example, wherein X is as recited including OSO.sub.3 CH.sub.3 and halide; U.S. Pat. No. 4,752,550, the disclosure of which is totally incorporated herein by reference, directed to toners and developers with inner salt charge additives and mixtures of such salts with other charge additives, see for example column 4; U.S. Pat. No. 32,883 (a reissue of U.S. Pat. No. 4,338,390), the disclosures of which are totally incorporated herein by reference, wherein toners with organic sulfonate and organic sulfate charge enhancing additives are illustrated, see columns 3, 4, and 5 to 10 for example; and U.S. Pat. No. 4,058,585 which discloses a process of extracting metals with organic solvent solutions of the salts of hydrogen ionic exchange agents, and quaternary ammonium compounds. Processes for preparing quaternary ammonium salts by an ion exchange or ion pair extraction method with soluble quaternary compounds is known, reference for example Phase Transfer Catalysis, Principles and Techniques, Academic Press, N.Y., 1978, especially page 76, C. M. Starks and C. Liotta, the disclosure of this textbook being totally incorporated herein by reference, and "Preparative Ion Pair Extraction", Apotekarsocieteten/Hassle, Lakemidel, pages 139 to 148, Sweden, 1974, the disclosure of which is totally incorporated herein by reference, which illustrates the preparation of certain bisulfates with water soluble ammonium salt reactants and a two-phase method wherein the product resides in the water phase.
Moreover, toner compositions with negative charge enhancing additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064, the disclosures of which are totally incorporated herein by reference. The '974 patent discloses negatively charged toner compositions comprised of resin particles, pigment particles, and as a charge enhancing additive ortho-halo phenyl carboxylic acids. Similarly, there are disclosed in the '064 patent toner compositions with chromium, cobalt, and nickel complexes of salicylic acid as negative charge enhancing additives.
There is illustrated in U.S. Pat. No. 4,404,271 a complex system for developing electrostatic images with a toner which contains a metal complex represented by the formula in column 2, for example, and wherein ME can be chromium, cobalt or iron. Additionally, other patents disclosing various metal containing azo dyestuff structures wherein the metal is chromium or cobalt include U.S. Pat. Nos. 2,891,939; 2,871,233; 2,891,938; 2,933,489; 4,053,462 and 4,314,937. Also, in U.S. Pat. No. 4,433,040, the disclosure of which is totally incorporated herein by reference, there are illustrated toner compositions with chromium and cobalt complexes of azo dyes as negative charge enhancing additives.
Illustrated in U.S. Pat. No. 4,937,157, the disclosure of which is totally incorporated herein by reference, are toner compositions comprised of resin, pigment or dye, and tetraalkyl, wherein alkyl, for example, contains from 1 to about 30 carbon atoms, ammonium bisulfate charge enhancing additives such as distearyl dimethyl ammonium bisulfate, tetramethyl ammonium bisulfate, tetraethyl ammonium bisulfate, tetrabutyl ammonium bisulfate, and preferably dimethyl dialkyl ammonium bisulfate compounds where the dialkyl radicals contain from about 10 to about 30 carbon atoms, and more preferably dialkyl radicals with from about 14 to about 22 carbon atoms, and the like. The aforementioned charge additives can be incorporated into the toner or may be present on the toner surface. Advantages of rapid admix, appropriate triboelectric characteristics, and the like are achieved with many of the toners of the aforementioned '157 patent, which toners can be prepared by melt blending. The tetrasubstituted ammonium salt selected can be heated in an appropriate solvent or solvents, such as water, in the presence of a stoichiometric amount of sulfuric acid. One typical process of preparation involves heating at an effective temperature of, for example, from about 40.degree. to about 100.degree. C. for an appropriate period of time, such as from about 5 to about 15 hours, the insoluble tetrasubstituted ammonium chloride or other halide, such as distearyl dimethyl ammonium chloride (DDACI), or the corresponding methyl sulfate salt, distearyl dimethyl ammonium methyl sulfate (DDAMS) in aqueous solution, about one molar equivalent in 85 molar equivalents of water and 10 molar equivalents of sulfuric acid in 56 molar equivalents of water. The crude product resulting after cooling to room temperature can be collected by filtration, and then purified by washing with various solvents such as acetone, followed by recrystallization from, for example, an appropriate solvent such as acetone or methanol, and the like. The resulting products, which can be identified by a number of techniques including melting point information, differential scanning calorimetry, infrared spectra, carbon, and proton nuclear magnetic resonance, ion chromotography, elemental analysis, and the like, can then be formulated into toners by melt blending.